P45-T Motor unit number estimation in facial muscles using the M Scan-Fit method

• Published in: Clinical neurophysiology Vol. 130; no. 7; p. e52
• Main Authors: Habeych, Miguel E., Trinh, Terry, Issar, Tushar, Y. Kwai, Natalie C., Krishnan, Arun V.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2019
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2019.04.408

The motor unit number estimation (MUNE) method is based on the concept of each motor unit (MU) having a specific activation threshold. M Scan is a technique in which the threshold of every MU from a muscle is obtained through a decreasing progression from supra to sub-threshold stimuli decreasing 0.2% each time, and drawn as function of intensity. In this study the M Scan technique was used to evaluate MU number in two muscles innervated by the facial nerve. We recruited 15 healthy volunteers [mean age: 33.27 ± 9.02 yrs (21–54), 26.67% females] to evaluate MUNE twice in the nasalis and depressor anguli oris (DAO) muscles. M scan was then fitted to an exponential model estimating the number of MUs in the tested muscle, based on the threshold, amplitude and relative spread of the threshold. The procedure was successfully performed in all subjects. The right hemi-face was always evaluated and 86.67% subjects were right handed. The initial study had a mean duration of 29.8 ± 6.26 min and 27.86 ± 5.17 the second occasion. Nasalis MU number: 37.73 ± 13.26 (22–72) on the initial test and 38.64 ± 16.6 (19–86) the second (p = 0.83). DAO MU number: 20.87 ± 4.92 (13–29) the first time vs. 24.21 ± 8.06 (11–39) the second (p = 0.08). Pearson’s inter-rater correlation coefficients (CC) were 0.67 for nasalis and 0.82 for DAO. Intra-rater CC: Nasalis: 0.91, DAO: 0.62. M Scan Fit-MUNE is an effective and reliable way to estimate MU number in muscles innervated by the facial nerve.